Quantifying the effects of alternative surface inlet protection strategies on water quality

Subsurface drainage systems with surface inlets are widely used to divert water in crop producing areas, but pose problems because they can allow unfiltered, sediment-laden water to travel quickly to other waterways. The project tested several modest, uncomplicated inlet protection practices with potential to keep nutrient and sediment flows in check

A design aid for determining width of filter strips

Watershed planners need a tool for determining width of filter strips that is accurate enough for developing cost-effective site designs and easy enough to use for making quick determinations on a large number and variety of sites. This study employed the process-based Vegetative Filter Strip Model to evaluate the relationship between filter strip width and trapping efficiency for sediment and water and to produce a design aid for use where specific water quality targets must be met. Model simulations illustrate that relatively narrow filter strips can have high impact in some situations, while in others even a modest impact cannot be achieved at any practical width. A graphical design aid was developed for estimating the width needed to achieve target trapping efficiencies for different pollutants under a broad range of agricultural site conditions. Using the model simulations for sediment and water, a graph was produced containing a family of seven lines that divide the full range of possible relationships between width and trapping efficiency into fairly even increments. Simple rules guide the selection of one line that best describes a given field situation by considering field length and cover management, slope, and soil texture. Relationships for sediment-bound and dissolved pollutants are interpreted from the modeled relationships for sediment and water. Interpolation between lines can refine the results and account for additional variables, if needed. The design aid is easy to use, accounts for several major variables that determine filter strip performance, and is based on a validated, process-based, mathematical model. This design aid strikes a balance between accuracy and utility that fills a wide gap between existing design guides and mathematical models

Impacts of conventional and diversified rotation systems on crop yields, profitability, soil functions and environmental quality

Comparisons were made among contrasting cropping systems within a long-term, large-scale field experiment in Boone County, Iowa. Combining crop diversity with lower herbicide inputs and non-transgenic crops was effective in reducing requirements for nitrogen fertilizer; maintaining or improving weed suppression, grain yields, and profi ts; and increasing several soil quality indicators

South Skunk River Watershed Rapid Watershed Assessment

The South Skunk River Rapid Watershed assessment provides initial estimates of where conservation investments would best address the Resource Priorities/Capabilities of landowners, conservation districts, and other community organizations and stakeholders. These assessments help landowners and local leaders set priorities and determine the best actions to achieve their goals to conserve soil and water resources

Boone River Watershed Rapid Watershed Assessment

The Boone River Rapid Watershed assessment provides initial estimates of where conservation investments would best address the resource priorities/capabilities of landowners, conservation districts, and other community organizations and stakeholders. These assessments help landowners and local leaders set priorities and determine the best actions to achieve their goals to conserve soil and water resources

Theme Overview: Agriculture and Water Quality in the Cornbelt: Overview of Issues and Approaches

Resource /Energy Economics and Policy, Q25,

Water quality benefits of perennial filter strips in row-cropped watersheds

Nonpoint source pollution is an increasingly serious problem in agricultural landscapes, especially as growing populations intensify pressures on a fixed land area for food and energy, and climate change threatens production stability. Vegetative filter strips (VFS) have been demonstrated as a practical strategy in reducing soil loss and nutrient transport from agricultural land. While restoration of native grassland on agricultural landscapes would improve environment quality, however, this practice is not feasible across large regions where local communities depend on agriculture. One alternative strategy for erosion control and water quality improvement is the incorporation of relatively small amounts of vegetative filter strips in strategic locations within agricultural landscapes

Comparing Agricultural Conservation Planning Framework (ACPF) practice placements for runoff mitigation and controlled drainage among 32 watersheds representing Iowa landscapes

Precision conservation planning tools can use high-resolution data to identify conservation practice-placement options for watershed improvement plans. Use of these tools across multiple watersheds could help to identify regional conservation strategies. This study evaluated practice-placement options determined using the Agricultural Conservation Planning Framework (ACPF) ArcGIS tools for controlled drainage (CD), contour buffer strips (CBS), water and sediment control basins (WASCOBs), and grassed waterways (GWWs) across 32 headwater hydrological unit code (HUC)12 watersheds in Iowa. The watersheds represented three Major Land Resource Areas (MLRAs) and four Agro-Hydrologic Landscape (AHL) classes, with four watersheds randomly chosen from each of eight combined MLRA-AHL landscape groupings. Placement options for the practices identified using the ACPF were quantified by watershed as densities (km km−2 of cropland) for GWWs, counts of proposed practice locations per square kilometer for CBS and WASCOBs, and as fractions of tile-drained land for CD. The influence of the landscape groupings on practice-placement densities among watersheds was tested using analysis of variance and contrast comparisons. Significant differences were found that led to nuanced interpretations. Differences attributed to slope steepness were captured by AHL classes, while differences attributed to slope shape and convergence were best captured by MLRA, which better segregated the watersheds based on landscape age and stream dissection. Grassed waterway placements showed minor differences among MLRAs but provided data to better inform the choices that ACPF users can make when running the GWW tool. The MLRA/AHL landscape classifications could be used together to develop effective regional conservation strategies using precision planning tools

Nutrient removal by prairie filter strips in agricultural landscapes

Nitrogen (N) and phosphorus (P) from agricultural landscapes have been identified as primary sources of excess nutrients in aquatic systems. The main objective of this study was to evaluate the effectiveness of prairie filter strips (PFS) in removing nutrients from cropland runoff in 12 small watersheds in central Iowa. Four treatments with PFS of different spatial coverage and distribution (No-PFS, 10% PFS, 10% PFS with strips, and 20% PFS with strips) were arranged in a balanced incomplete block design across four blocks in 2007. A no-tillage two-year corn (Zea mays L.) –soybean (Glycine max [L.] Merr.) rotation was grown in row-cropped areas beginning in 2007. Runoff was monitored by H flumes, and runoff water samples were collected during the growing seasons to determine concentrations of nitrate-nitrogen (NO3-N), total nitrogen (TN) and total phosphorus (TP) through 2011. Overall, the presence of PFS reduced mean annual NO3-N, TN, and TP concentrations by 35%, 73%, and 82%, respectively, and reduced annual NO3-N, TN, and TP losses by 67%, 84%, and 90%, respectively. However, the amount and distribution of PFS had no significant impact on runoff and nutrient yields. The findings suggest that utilization of PFS at the footslope position of annual row crop systems provides an effective approach to reducing nutrient loss in runoff from small agricultural watersheds

Effects of native perennial vegetation buffer strips on dissolved organic carbon in surface runoff from an agricultural landscape

Dissolved organic carbon (DOC) constitutes a small yet important part of a watershed’s carbon budget because it is mobile and biologically active. Agricultural conservation practices such as native perennial vegetation (NPV) strips will influence carbon cycling of an upland agroecosystem, and could affect how much DOC enters streams in runoff, potentially affecting aquatic ecosystems. In a study conducted in Iowa (USA), four treatments with strips of NPV varying in slope position and proportion of area were randomly assigned among 12 small agricultural watersheds in a balanced incomplete block design. Runoff samples from 2008 to 2010 were analyzed for DOC and correlated with flow data to determine flow weighted DOC concentrations and loads. Data were analyzed for the entire 3 years, annually, seasonally, monthly, by flow event size and for one extreme storm event. Overall we found few differences in DOC concentration with the exception that concentrations were greater in the 10 % NPV at the footslope watersheds than the 20 % NPV in contours watersheds over the 3 years, and the 100 % agricultural treatment had higher DOC concentrations than all NPV treatments during the one extreme event. Because the NPV treatments reduced runoff, DOC export tended to be highest in the 100 % agricultural watersheds over the 3 years and during high flows. We also compared two watersheds that were restored to 100 % NPV and found decreases in DOC concentrations and loads indicating that complete conversion to prairie leads to less watershed DOC export. Regression results also support the contention that increases in the percentage of NPV in the watershed decreases watershed export of DOC. Further analysis indicated that DOC concentrations were diluted as flow event size increased, independent of any treatment effects. It appears groundwater sources become an important component to flow as flow event size increases in these watersheds